A "water year" with two troubling features — a slow start to winter’s mountain snowpack and a very hot, very dry summer — wound up in surprising ways.

In short, despite those two big factors, supplies for Denver Water remained strong and the 2023-24 water year, having opened with drama, closed as a quiet success.

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What’s a water year? It’s that span from Oct. 1 through Sept. 30 that water utilities, hydrologists and other experts use to track the flow of annual precipitation, from early snowfall through runoff and the months of water use on farm fields and in cities.

And the water year ending last month, on Sept. 30, 2024, clocked in as a good one for Denver Water.

After the slow start, snowpack improved over late winter and spring, reservoirs filled and spilled and customers mostly stuck to watering rules, even amid a scorching, low-rain summer in Denver Water’s service area.

Some high notes from the past 12 months:

• It marked the first year since 2019 that peak snowpack in both of Denver Water’s key river basins was above normal: 101% in the South Platte River basin and 124% in the Colorado River basin.
• Denver Water’s reservoirs hit capacity, always an important outcome. And a two of those — Cheesman and Strontia Springs — spilled with excess water for the first time since 2019. Two others, Dillon and Williams Fork, spilled for the second straight year.
• Supplies were so strong on the Front Range that Denver Water kept Roberts Tunnel — the conveyance that brings water from Dillon Reservoir on the West Slope — turned off for six months, from January to mid-July. The Moffat Tunnel that brings water from the Fraser River to Gross Reservoir was offline for three weeks in June. 

It marked a remarkable turnaround from some big obstacles earlier in the year.

By mid-January 2024, anemic snowpack was ranked among the five worst totals for that time of year on record.

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And a tough summer awaited. Denver Water’s records put the summer of 2024 as the fifth-hottest in the region. And precipitation was weak, ranking fourth worst in the utility’s service area. 

But after that slow start, the snowpack rallied. Big snows occurred in late January, followed by normal snows in February and a big March storm that pushed snowpack numbers up, especially in the North Fork of the South Platte River.

Then, in a big surprise, the storms kept coming. Not only in April but in May, also, weeks beyond the point snowpack typically stops building. 

More good news followed. Spring soil moisture was in good shape, so water stayed in streams and filled reservoirs instead of soaking into bone-dry ground, a frequent problem in recent years.

Then, customers did their part, largely adhering to watering rules that kept water use stable even amid such a hot and dry summer.

Daily use in Denver Water’s service area never soared above average and total summer demand from customers hewed close to normal. 

“Customers continue to understand the basics: Don’t water in the heat of the day, turn off your irrigation after rainstorms. Keep your watering to two or, at most, three days a week,” said Nathan Elder, Denver Water’s manager of water supplies.

“And we are seeing many customers take even more important long-term steps, like adjusting their landscapes with water-wise plants and grasses and reducing the amount of their traditional, thirstier turfgrass.”

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For Elder, the success story of the 2024 water year was how well Denver Water was able to manage its system to maximize flows for recreation and the environment.

Healthy supplies meant more water releases from Dillon that bolstered rafting in the Blue River. Good supplies also helped support rafting on the North Fork for the annual BaileyFest event. It also kept reservoir elevations high for flatwater recreation, such as boating and paddleboarding.

It also allowed releases to help aquatic environments, such as keeping stream temperatures in a safe range for fish in the Fraser River and providing flushing flows to improve fish habitat on the South Platte. 

Supplies also helped ensure Denver Water could provide water downstream on the Colorado River to support endangered fish above Grand Junction. 

“After a nerve-wracking start, the water year improved in a hurry,” Elder said. “Full reservoirs and good runoff give us the flexibility to move water around in a way that helps a lot of interests while serving our customers.”

Now, as the new water year kicks off, the watch for precipitation begins. 

And we enter the new water year with good news: Denver Water reservoirs begin the 2024-25 water year with good supplies. But a dry summer in the region has left dry, thirstier soils that could drink up melting snow next spring. That could make 2025 trickier. 

The wait, and watch, is on.

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